feat: 升级到 lipgloss/bubbletea v2，实现翻译卡片组件

- 升级 charm.land/lipgloss/v2 v1.1.0 -> v2.0.2
- 升级 charm.land/bubbletea/v2 v1.3.10 -> v2.0.2
- 升级 charm.land/bubbles/v2 -> v2.1.0
- 新增翻译卡片组件：元信息行(Tokens/耗时/模型)、用户输入(碳黑背景)、翻译结果
- 卡片组件间距 5px
- 重构 model.go 适配 v2 API
- 更新 keys.go, messages.go, styles.go

internal/tui/keys.go

@@ -0,0 +1,48 @@
+package tui
+
+import (
+	"charm.land/bubbles/v2/key"
+)
+
+type KeyMap struct {
+	Quit         key.Binding
+	Clear        key.Binding
+	SwitchLang   key.Binding
+	ScrollUp     key.Binding
+	ScrollDown   key.Binding
+	ScrollTop    key.Binding
+	ScrollBottom key.Binding
+}
+
+func NewKeyMap() KeyMap {
+	return KeyMap{
+		Quit: key.NewBinding(
+			key.WithKeys("ctrl+c", "esc"),
+			key.WithHelp("Ctrl+C", "退出"),
+		),
+		Clear: key.NewBinding(
+			key.WithKeys("ctrl+l"),
+			key.WithHelp("Ctrl+L", "清空输入"),
+		),
+		SwitchLang: key.NewBinding(
+			key.WithKeys("ctrl+t"),
+			key.WithHelp("Ctrl+T", "切换语言"),
+		),
+		ScrollUp: key.NewBinding(
+			key.WithKeys("up", "ctrl+up"),
+			key.WithHelp("↑/Ctrl+↑", "上滚"),
+		),
+		ScrollDown: key.NewBinding(
+			key.WithKeys("down", "ctrl+down"),
+			key.WithHelp("↓/Ctrl+↓", "下滚"),
+		),
+		ScrollTop: key.NewBinding(
+			key.WithKeys("home"),
+			key.WithHelp("Home", "顶部"),
+		),
+		ScrollBottom: key.NewBinding(
+			key.WithKeys("end"),
+			key.WithHelp("End", "底部"),
+		),
+	}
+}